<title>Recent progress in the hard-tube MILO experiment</title>

The Hard-Tube MILO (Magnetically Insulated transmission Line Oscillator) is a gigawatt-class L-band high power microwave tube driven by a 500 kV, 60 kA electron beam. It is nearly identical to the MILO reported by Calico et al., with the principle difference being that the Hard-Tube MILO has been constructed using conventional-tube brazing techniques for the rf joints, while the earlier version of MILO used finger-stock connections for the rf joints. This paper reports on recent experimental improvements to the tube that have allowed us to generate 1.5 - 2.0 GW pulses of 175 ns duration; a 2.5 times improvement in the pulse width over the original tube. In addition, we report on experiments to identify the breakdown mechanism in the vacuum radome for the Vlasov antenna used to radiate the microwave pulse. Finally, details of an optimized version of the Hard-Tube MILO that should allow us to generate over 3.0 GW are presented.